Process for removing polar impurities from hydrocarbons and mixtures of hydrocarbons

ABSTRACT

This invention relates to a process for removing polarizable impurities from hydrocarbons and mixtures of hydrocarbons using ionic liquids as an extraction medium for reducing the degree of contamination of the hydrocarbon or mixture of hydrocarbons to a low or very low level.

DESCRIPTION

This invention relates to a process for removing polarizable impurities from hydrocarbons and mixtures of hydrocarbons using ionic liquids as an extraction medium for reducing the degree of contamination of the hydrocarbon or mixture of hydrocarbons to a low or very low level.

PRIOR ART AND OBJECT OF THE INVENTION

The separation of polarizable impurities from hydrocarbons or mixtures of hydrocarbons to reduce their contents to ppm levels is of great technical importance, but is often found to pose problems. The importance of such purification processes resides in the fact that many polarizable impurities in hydrocarbons and mixtures of hydrocarbons limit their technical usefulness because they have either disturbing effects on the actual technical process or result in by-products which are undesirable from an environmental point of view. Important examples thereof include the separation of sulfur and nitrogen components from fuels for reducing the SO₂ emissions, or the reduction of chlorine-containing compounds from motor oils to avoid corrosion problems.

The deep desulfurization of fuels to achieve very low sulfur contents (>50 ppm) is a great problem in the production of fuel. The legal conditions currently designate a reduction of the sulfur content in gasoline and diesel fuels to 50 ppm for the year 2005 within the European Union. Propositions by the German government already aim at a reduction to 10 ppm in the year 2003 (W. Bonse-Geuking, Erdbl Erdgas Kohle, 116, 9 (2000) 407). According to the current state of the art, the separation of sulfur-containing compounds is effected by catalytic hydrogenation in refineries (I. Pachano, J. Guitian, O. Rodriguez, J. H. Krasuk (Intevep, S. A.), U.S. Pat. No. 4,752,376 (1988), Jr. Hensley, L. Albert, L. M. Quick (Standard Oil Company), U.S. Pat. No. 4,212,729 (1980), S. B. Alpert, R. H. Wolk, M. C. Chervenak, G. Nongbri (Hydrocarbon Research, Inc.), U.S. Pat. No. 3,725,251 (1971), G. R. Wilson (Gulf Research & Development Company), U.S. Pat. No. 3,898,155 (1975), Y. Fukui, Y. Shiroto, M. Ando, Y. Homma (Chiyoda Chemical Engineering & Construction Co., Ltd.), U.S. Pat. No. 4,166,026 (1979), R. H. Fischer, J. Ciric, T. E. Whyte (Mobil Oil Corporation), U.S. Pat. No. 3,867,282 (1975), J. G. Gatsis (Universal Oil Products Company), U.S. Pat. No. 3,859,199 (1975), L. K. Riley, W. H. Sawyer (Esso Research and Engineering Company), U.S. Pat. No. 3,770,617 (1973), C. E. Adams, W. T. House (Esso Research and Engineering Company), U.S. Pat. No. 3,668,116 (1972)). The separation of the hydrogen sulfide formed is effected by amine washers (W. W. Kensell, M. P. Quinlan, The M.W. Kellogg Company Refinery Sulfur Management, in: R. A. Meyers (Ed.), Handbook of Petroleum Refining Processes, New York, San Francisco, Washington, D.C., Auckland, Bogota, Caracas, Lisbon, London, Madrid, Mexico City, Milan, Montreal, New Delhi, San Juan, Singapore, Sydney, Tokyo, Toronto: McGraw-Hill, 1996, 11.3). Another method is the UOP Merox process. In this process, the mercaptans present in the fuel are reacted with oxygen to form disulfides in the presence of an organometallic catalyst at low temperatures in an alkaline medium (D. L. Holbrook, UOP Merox Process, in: R. A. Meyers (Ed.), Handbook of Petroleum Refining Processes, New York, San Francisco, Washington, D.C., Auckland, Bogota, Caracas, Lisbon, London, Madrid, Mexico City, Milan, Montreal, New Delhi, San Juan, Singapore, Sydney, Tokyo, Toronto: McGraw-Hill, 1996, 11.29).

Halogenated impurities in hydrocarbons and mixtures of hydrocarbons cause corrosion problems in engineering, and therefore, their content must be usually reduced down to a range of a few ppm. Technically, this is achieved by catalytic hydrogenation or electrolytic dehalogenation (G. Scharfe, R.-E. Wilhelms (Bayer Aktiengesellschaft), U.S. Pat. No. 3,892,818 (1975), J. Langhoff, A. Jankowski, K.-D. Dohms (Ruhrkohle AG), U.S. Pat. No. 5,015,457 (1991), W. Dohler, R. Holighaus, K. Niemann (Veba Oel Aktiengesellschaft), U.S. Pat. No. 4,810,365 (1989), F. F. Oricchio (The Badger Company, Inc.), U.S. Pat. No. 3,855,347 (1974), R. W. La Hue, C. B. Hogg (Catalysts and Chemicals, Inc.), U.S. Pat. No. 3,935,295 (1976), F. Rasouli, E. K. Krug (ElectroCom Gard, Ltd.), U.S. Pat. No. 5,332,496 (1994), H. J. Byker (PCB Sandpiper, Inc.), U.S. Pat. No. 4,659,443 (1987), ]J. A. F. Kitchens (Atlantic Research Corporation), U.S. Pat. No. 4,144,152 (1979)).

Ionic liquids have been known for many years (P. Wasserscheid, W. Keim, Angew. Chem., 112 (2000) 3926; T. Welton, Chem. Rev., 99 (1999) 2071; J. D. Holbrey, K. R. Seddon, Clean Products and Processes, 1 (1999), 223). They are characterized by being liquids which exclusively consist of ions. Important properties include their solubility properties which can be adjusted within wide limits by varying the cation and/or anion, and their immeasurably low vapor pressure. Numerous ionic liquids are not completely miscible with hydrocarbons and mixtures of hydrocarbons, i.e., the formation of two-phase or multi-phase systems occurs (P. Wasserscheid, W. Keim, Angew. Chem., 112 (2000) 3926).

OUR INVENTION

Our invention is based on the surprising finding that the content of polarizable impurities in a hydrocarbon or mixture of hydrocarbons can be significantly reduced by extracting the hydrocarbon or mixture of hydrocarbons with an ionic liquid or a mixture of ionic liquids if the ionic liquid employed exhibits a miscibility gap with said hydrocarbon or mixture of hydrocarbons. Thus, our invention represents a novel and extremely efficient solution to the above mentioned problems in the separation of polarizable impurities from hydrocarbons or mixtures of hydrocarbons.

For the removal of sulfur-containing impurities from hydrocarbons or mixtures of hydrocarbons, the innovation according to this invention offers a successful alternative which is significantly superior to the hydrogenation methods according to the current state of the art with respect to hydrogen consumption, operational and investment costs. For example, if the process according to this invention is applied to the desulfurization of diesel fuel, the extraction of the sulfur-containing impurities by means of ionic liquids is substituted for the currently applied hydrogenation reactions. The process according to this invention is not limited to any particular classes of sulfur-containing compounds, but universally reduces the content of sulfur-containing compounds in the processing of petrol fractions. By several extraction steps the residual sulfur content can be reduced down to below the detection limit of the analytical method employed (<1 ppm). Thus, the process according to this invention represents a novel possibility for significantly reducing the sulfur content in different fuels and to clearly reduce it below the future legal level of 50 ppm.

Re-extraction of the sulfur compound from the ionic liquid in terms of a regeneration of the ionic liquid used as an extractant is also possible. Particularly suitable are media which also exhibit a miscibility gap with the ionic liquid, but are very highly volatile, such as short-chained alkanes in a liquid or supercritical state or liquid or supercritical CO₂. The charged re-extractant can be recovered by distillation. The extracted impurities are left behind together with low amounts of the material employed or the mixture of materials employed. The ionic liquid purified by re-extraction can be recycled into the desulfurization process.

In the dehalogenation the novel process according to this invention circumvents the classical drawbacks of conventional dehalogenation by hydrogenation (high pressure, high temperatures, release of corrosive HCl gas).

EXAMPLES

1. Desulfurization of Dibenzothiophene in n-dodecane

Using the desulfurization of the model component dibenzothiophene dissolved in n-dodecane as an example, the performance of our invention shall be demonstrated. FIG. 1 shows the structures of some of the ionic liquid employed and the thus achieved sulfur contents after one extraction starting from a sulfur content of 500 ppm. In this case, the dibenzothiophene serves as a model component for a compound which is difficult to desulfurize by the classical dehydrogenation method.

Examples of Ionic Liquid Employed

(a) 1-Butyl-3-methylimidazolium tetrachloroaluminate; (b) 1-ethyl-3-methylimidazolium tetrachloroaluminate; (c) diethylcyclohexylammonium methanesulfonate/tributylammonium methylmethanesulfonate; (d) dodecyltrimethylammonium tetrachloroaluminate; (e) trioctylmethylammonium tetrachloroaluminate; (f) diethylmethylcyclohexylammonium methansulfonate/tributylmethylammonium methanesulfonate; (g) 1-butyl-3-methylimidazolium BTA; (h) 1,3-dimethylimidazolium methanesulfonate.

The ionic liquid and the model oil are intensively stirred at a mass ratio of 1 to 5 for 15 minutes at room temperature or at 60° C. in the case of (c) and (f) since these are solids at room temperature. Thereafter, the model oil is separated from the two-phase mixture, and the sulfur content is determined by combustion analysis.

2. Multistep Desulfurization of Dibenzothiophene in n-dodecane

Here it is shown that a further significant reduction of the sulfur content of the model component dibenzothiophene can be achieved by means of a multistep extraction with ionic liquids. Furthermore it is shown that the different ionic liquids in part have clearly different suitabilities. The process itself is the same as in Example 1. However, the model oil having been desulfurized once is again reacted respectively with fresh ionic liquid in second, third etc. steps. The results are shown in Table 1. TABLE 1 Results of multisteo extractions of model oil (500 ppm) with ionic liquids Sulfur content [ppm] after step Compound 1 2 3 4 (a) 260 120 55 25 (c) 305 195 120 65 (f) 335 210 130 85 (h) 450 420 405 3. Desulfurization of Real Fuels

The following Examples show that a transfer of the experiments with the model component dibenzothiophene on the desulfurization with ionic liquids to complex real systems is possible. Thus, the same procedure is employed as in Example 2. As an example of a fuel a predesulfurized diesel fraction with a sulfur content of 375 ppm is used. Some results are summarized in Table 2. TABLE 2 Results of multistep extractions of diesel fuel (375 ppm) with ionic liquids Sulfur content [ppm] after step Compound 1 2 3 4 8 (a) 220 160 130 100 40 (c) 325 290 250 225 (f) 330 300 

1. A process for removing polar impurities from hydrocarbons and mixtures of hydrocarbons, characterized in that extraction of said polar impurities is effected with ionic liquids.
 2. The process according to claim 1, characterized in that the ionic liquid employed is an ionic liquid of general formula [A]_(n) ⁺[Y]^(n−), wherein n=1 or 2; and the anion [Y]^(n−) is selected from the group consisting of tetrafluoroborate ([BF₄]⁻), tetrachloroborate ([BCl₄]⁻), hexafluorophosphate ([PF₆]⁻), hexafluoroantimonate ([SbF₆]⁻), hexafluoroarsenate ([AsF₆]⁻), tetrachloroaluminate ([AlCl₄]⁻), trichlorozincate ([ZnCl₃]⁻), dichlorocuprate ([CuCl₂]⁻, sulfate ([SO₄]²⁻), carbonate ([CO₃]²⁻), fluorosulfonate, [R′—COO]⁻, [R′—SO₃]⁻, [R′—SO₄], [tetrakis(3,5-bis(trifluoromethyl)phenyl)borate] ([BARF]) or [(R′—SO₂)₂N]⁻, and R′ is a linear or branched aliphatic or alicyclic alkyl containing from 1 to 12 carbon atoms, or a C₅-C₁₈ aryl, C₅-C₁₈-aryl-C₁-C₆-alkyl or C₁-C₆-alkyl-C₅-C₁₈-aryl residue which may be substituted with halogen atoms; the cation [A]⁺ is selected from quaternary ammonium cations of general formula [NR¹R²R³R]⁺, phosphonium cations of general formula [PR¹R²R³R]⁺, imidazolium cations of general formula

wherein the imidazole nucleus may be substituted with at least one group selected from C₁-C₆ alkyl, C₁-C₆ alkoxy, C₁-C₆ aminoalkyl, C₅-C₁₂ aryl or C₅-C₁₂-aryl-C₁-C₆-alkyl groups; pyridinium cations of general formula

wherein the pyridine nucleus may be substituted with at least one group selected from C₁-C₆ alkyl, C₁-C₆ alkoxy, C₁-C₆ aminoalkyl, C₅-C₁₂ aryl or C₅-C₁₂-aryl-C₁-C₆-alkyl groups; pyrazolium cations of general formula

wherein the pyrazole nucleus may be substituted with at least one group selected from C₁-C₆ alkyl, C₁-C₆ alkoxy, C₁-C₆ aminoalkyl, C₅-C₁₂ aryl or C₅-C₁₂-aryl-C₁-C₆-alkyl groups; and triazolium cations of general formula

wherein the triazole nucleus may be substituted with at least one group selected from C₁-C₆ alkyl, C₁-C₆ alkoxy, C₁-C₆ aminoalkyl, C₅-C₁₂ aryl or C₅-C₁₂-aryl-C₁-C₆-alkyl groups; and the residues R¹, R², R³ are independently selected from the group consisting of hydrogen; linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 20 carbon atoms; heteroaryl, heteroaryl-C₁-C₆-alkyl groups having from 3 to 8 carbon atoms in the heteroaryl residue and at least one heteroatom selected from N, O and S which may be substituted with at least one group selected from C₁-C₆ alkyl groups and/or halogen atoms; aryl, aryl-C₁-C₆-alkyl groups having from 5 to 12 carbon atoms in the aryl residue which may be optionally substituted with at least one C₁-C₆ alkyl group and/or halogen atom; an the residue R is selected from linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 20 carbon atoms; heteroaryl-C₁-C₆-alkyl groups having from 3 to 8 carbon atoms in the aryl residue and at least one heteroatom selected from N, O and S which may be substituted with at least one C₁-C₆ alkyl group and/or halogen atom; aryl-C₁-C₆-alkyl groups having from 5 to 12 carbon atoms in the aryl residue which may be optionally substituted with at least one C₁-C₆ alkyl group and/or halogen atom; by alkylation of the underlying amines, phosphines, imidazoles, pyridines, triazoles and pyrazoles with a halide RX and replacement of the halide anions X⁻ with the above defined anion [Y]⁻ or [Y]²⁻, characterized in that the process is carried out without isolation of the intermediate products.
 3. The process according to claims 1 to 2, characterized in that the compounds which are to be removed are sulfur-containing compounds.
 4. The process according to claims 1 to 2, characterized in that the compounds which are to be removed are halogen-containing compounds.
 5. The process according to claims 1 and 2 as well as 3 or 4, characterized in that the extraction is performed within a temperature range of from −150° C. to 500° C., preferably within a range of from −25° C. to 200° C., more preferably from 0° C. to 150° C.
 6. The process according to claims 1-5, characterized in that both the extraction and the separation from the hydrocarbon or mixture of hydrocarbons are effected within a temperature range in which the ionic liquid is in liquid form.
 7. The process according to claims 1-5, characterized in that the extraction is effected within a temperature range in which the ionic liquid is in liquid form, and the separation from the hydrocarbon or mixture of hydrocarbons is effected within a temperature range in which the ionic liquid is in solid form.
 8. The process according to claims 1 to 5 as well as 6 or 7, characterized in that the amount of ionic liquid added has a mass proportion within a range of from 0.01 to 99%, preferably from 0.1 to 50%, most suitably from 0.5 to 30%.
 9. The process according to claims 1-5 and 8 as well as 6 or 7, characterized in that the extraction is performed in a mixer-settler unit.
 10. The process according to claims 1 to 4 and 6, or 1 to 3 and 5 to 6, characterized in that the extraction is performed in a tray column.
 11. The process according to claims 1-5 and 8 as well as 6 or 7, characterized in that the extraction is performed in a bubble column.
 12. The process according to claims 1-5 and 8 as well as 6 or 7, characterized in that the extraction is performed in a packed column.
 13. The process according to claims 1-5 and 8 as well as 6 or 7, characterized in that the extraction is performed in a packed column.
 14. The process according to claims 1-5 and 8 as well as 6 or 7, characterized in that the extraction is performed in a disk separator.
 15. The process according to claims 1-5 and 8 as well as 6 or 7, characterized in that the extraction is performed in a rotating disk column.
 16. The process according to claims 1-5 and 8 as well as 6 or 7, characterized in that the extraction is performed in a vibrating plate column.
 17. The process according to claims 1 to 16, characterized in that the separation of the extracted impurities from the ionic liquid is effected by a hydrocarbon or mixture of hydrocarbons.
 18. The process according to claims 1 to 17, characterized in that the separation of the extracted impurities from the ionic liquid is effected by an organic compound or mixture of organic compounds, wherein said organic compound or mixture of organic compounds has a miscibility gap with the ionic liquid.
 19. The process according to claims 1 to 18, characterized in that the separation of the extracted impurities from the ionic liquid is effected by liquid carbon dioxide.
 20. The process according to claims 1 to 18, characterized in that the separation of the extracted impurities from the ionic liquid is effected by supercritical carbon dioxide.
 21. The process according to claims 1 to 18, characterized in that the separation of the extracted impurities from the ionic liquid is effected by liquid propane.
 22. The process according to claims 1 to 18, characterized in that the separation of the extracted impurities from the ionic liquid is effected by supercritical propane.
 23. The process according to claims 1 to 18, characterized in that the separation of the extracted impurities from the ionic liquid is effected by steam distillation.
 24. The process according to claims 1 to 18, characterized in that the separation of the extracted impurities from the ionic liquid is effected by distillation or sublimation.
 25. The process according to claims 1 to 18, characterized in that the separation of the extracted impurities from the ionic liquid is effected by hydrogenating the impurities in the ionic liquid followed by removing the reaction products by processes according to claims 19 to
 24. 26. The process according to claims 1 to 18, characterized in that the separation of the extracted impurities from the ionic liquid is effected by oxidizing the impurities in the ionic liquid followed by removing the reaction products by processes according to claims 19 to
 24. 27. The process according to claims 1 to 18, characterized in that the separation of the extracted impurities from the ionic liquid is effected by absorption to an absorbent.
 28. The process according to claims 1 to 27, characterized in that the absorbent employed for the separation of the extracted impurities from the ionic liquid is active charcoal.
 29. The process according to claims 1 to 27, characterized in that the absorbent employed for the separation of the extracted impurities from the ionic liquid is a zeolite.
 30. The process according to claims 1 to 18, characterized in that the extracted impurities remain in the ionic liquid, and the ionic liquid is reactivated by adding appropriate components.
 31. The process according to claims 1 to 18, characterized in that the extracted impurities in the ionic liquid are decomposed by electrolysis and separated off by processes according to claims 19 to
 24. 